Microscopic aspects of surface deformation and fracture of high density polyethylene

Abstract

Microstructural evolution during plastic deformation of high density polyethylene was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques as a function of strain and strain rate. At low strain rates of tensile test, wedging was the dominant mode of deformation and produced fibrillated fracture. At higher strain rates, wedging was reduced and crazing was the dominant micromechanism of deformation. The final fracture was a combination of crazing/tearing and fibrillation. The micromechanisms of deformation and fracture are sensitive to strain rate. The domains of micromechanisms of deformation are depicted in terms of strain rate–strain diagrams providing a perspective of the domains of the deformation processes occurring in different strain rate–strain regimes. Atomic force microscopy was applied to study the mechanical response in wedge and craze modes of deformation, and quantify the surface relief. Atomic force microscopy indicated that wedge mode of deformation involved drawing and grouping or close packing of lamellae, while crazing was characterized by stretching, merging and splitting of lamellae, and formation of microvoids between the split lamellae. The surface relief associated with wedge was relatively less in comparison to craze deformed region.